The long-term objective of this work is to develop improved methods for identifying and characterizing large molecules, and to apply these methods to various biological problems. Time-of- flight techniques will be used to determine the mass spectra of ions ejected from organic compounds by particle bombardment (SIMS), as well as ions produced by resonance-enhanced multiphoton ionization (REMPI) of described neutral molecules. Samples will be prepared for mass spectrometric examination by liquid chromatography. Specifically it is proposed: 1. To make improvements in instrumentation and technique, including further modifications to a reflecting time-of-flight spectrometer to improve its resolution and to enable examination of ions produced by REMPI. 2. To carry out studies on the basic physics of the secondary ion emission process and REMPI, so as to obtain a better understanding of these processes and to facilitate their application to biological problems. 3. To apply time-of-flight mass spectrometry and its combination with liquid chromatography (LC/MS) to various samples of biological interest, in particular to nucleotides and natural mixtures of neuropeptides.